nsdictionary copy vs mutable copy

Question

I have

NSMutableDictionary *myDictionary = [[NSMutableDictionary alloc] init];
id dict = [myDictionary copy];

but is dict now just a regular NSDictionary? Or is it a copy of the NSMutableDictionary?

Also, is there any way to go from mutable to non-mutable?

Williham Totland · Accepted Answer · 2012-04-22T18:11:33.503

18

There are two methods involved here; -copy and -mutableCopy.

If the class holds a distinction; -copy always creates an immutable copy; and -mutableCopy always creates a mutable copy.

If the class holds no distinction; -copy always creates a true copy.

So yes, dict is now an NSDictionary, containing the objects in the dictionary.

edited Apr 22 '12 at 18:11

answered Apr 22 '12 at 17:49

Williham Totland

1

Minor correction: `copy` does not create a _deep copy_, so the objects in the copied dictionary will be the same as those in the original one, not copies. – omz Apr 22 '12 at 18:07
@omz: Does that also apply if the contents of the dictionary adopt `NSCopying`? – Williham Totland Apr 22 '12 at 18:10
The Cocoa collection classes always do a shallow copy for the `-copy` method. – Ken Thomases Apr 22 '12 at 18:15
4

Yes, you would have to explicitly use `initWithDictionary:copyItems:` to create a deep copy. – omz Apr 22 '12 at 18:15
@WillihamTotland: Yes. The objects in the dictionary make no difference; the copy is always shallow. – Peter Hosey Apr 22 '12 at 18:15
@Williham Totland : hi..can you please explain what do you mean by " class holds distinction".... thanks in advance. – Nirav Valera Nov 28 '12 at 13:44
1

@Cultor: I feel the meaning of the word should be clear from my answer. – Williham Totland Nov 30 '12 at 02:09
1

@Williham Totland : hi, actually I'm a beginner, so didn't understand. – Nirav Valera Dec 01 '12 at 12:39

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